Japan is one of the countries where congenital dislocation of the hip joint occurs frequently, as appears to be the case also with north American and Canadian Indians and north European Lapps and in Italy and West Germany. This disease is quite serious among congenital diseases of babies. As for the frequency of the disease, including incomplete dislocation, malformation of the acetabular tegmen and other mild forms of the disease, in addition to complete dislocation, it is estimated to be approximately 1 in every 20.
In the above-mentioned countries where congenital dislocation of the hip joint occurs frequently, there is a habit of stretching the baby's legs and wrapping up the same, and in Japan there was a period when the baby's legs were squeezed by a wrapping diaper or triangular diaper, thus keeping the hip joints stretched.
From such facts, it has been found that most of congenital dislocation of the hip joint is attributable to preventing free movement of the baby's legs and keeping them stretched in quite early stages of infancy. The incidence of congenital dislocation was sharply decreased by the use of a crotch diaper and a loose garment for babies immediately after they were born, which clothing does not interfere with the movement of the baby's legs and allows the legs to spread in natural form, i.e., the hip joints are permitted to bend and spread like those of a "frog".
The factors which prevent a natural cure of congenital dislocation of the hip joint and aggravate the disease are not limited to diapers and garments. The strap formerly used to carry a baby on the back has almost gone out of use with changes in life-style and the band for carrying a baby under the arm has come into frequent use. In the case of the band, the legs are stretched with the hips supported and the whole body is elongated and constrained, the baby often being forced to remain in such an unnatural position for a long time.
The modern baby carriage began to be used after the end of World War II, and baby carriages now in frequent use are not of the type in which a baby lies stretched but of the type in which a chair-type hammock is suspended. Further, such baby carriages have been reduced in size, with the hammock changed into one having a bag-like seat portion just as the strap changed into the band.
It is believed that in this manner, the changes in the environment for raising babies have resulted in abnormally pressing the hip joints of babies, leading to dislocation of the hip joint.
Dislocation of the hip joint is detected by a regular medical examination at health centers and the patients' parents are advised how to take care of their babies. In this case, the baby is treated so that it may be able to bend its legs and spread freely.
If the baby's hip joints are dislocated, the baby will limp as it learns to walk. However, where the symptoms of dislocation are slight or even if the affected part gets capsulated with insufficient medical care, there is no direct influence on life. As a result, there are many cases in which the affected part is left as it is. In such condition, if the baby grows, it will feel pain in the hip joints and limp, with the movement of the legs becoming worse, and finally the disease advances to uncurable, coxarthritis deformans.
Based on the way of thinking described above, the development of a nursing implement which adjusts the posture of a baby to its most natural body form and which does not interfere with its free movement is desired.